Sažetak
The neat alcohols exhibit local heterogeneity which is results of the different organization of hydrogen-bonded and hydrophobic sites. The amphyphilicity of alcohol-molecule leads to typical clusters-like associations, where oxygen atoms through hydrogen bonding form open chains or globular clusters, while methyl groups are homogeneously distributed around these clusters [1]. The status of neat water is more complex: the structural properties indicate clustering with the characteristic sizes of the near-neighbour contact. In this study, we show that a simple core-softened interaction, namely a soft-core 1/r12 interaction together with Gaussian repulsion, is able to reproduce the major features of radial distribution function and the structure factor of water, hence suggesting that such repulsive interaction is able to mimic the structure of real water [2]. We use both Monte Carlo simulations and the well known Percus-Yevick (PY) and Hypernetted-chain (HNC) integral equation theories. This study indicates that the structure of liquid water can be seen as the result of the two competing interactions, with two length scales: the diameter of the oxygen atom and the length of the hydrogen bond. It also indicates that this competition is not confined to near-neighbours, but is very (possibly infinitely) long ranged. This is indeed confirmed by the outcome of the integral equation studies. The HNC equation is able to reproduce the structure with puzzling accuracy -in view of its lesser accuracy when the Gaussian core is removed. In contrast, the PY equation has no solution for this state point ; it does at higher temperatures, but with dramatic inaccuracy, a result of its insufficient diagrammatic structure. Therefore, even if simple alcohols have more richer structure including various topologies of clusters, water in its simplicity holds more intriguing features, which remain -to date- largely unexplored. [1]. Zoranic L., Sokolic F. and Perera A., “Microstructure of neat alcohols: A molecular dynamics study“, Journal of Chemical Physics, 127, 024502-10 (2007) [2] Perera A., Rispe A., Zoranic L., Mazighi R. and Sokolic F., “Water-like structure with repulsive double-core interactions“, Molecular Physics, in press